In general, a reference prior art type of electric motor comprises a casing having inside a stator of the wound type, rigidly constrained to the casing, and a rotor, for example with permanent magnets, rotatably constrained to the casing.
An electronic module or control electronics, connected to the stator, is inserted in the casing for supplying power to the stator.
A cap closes the casing to form a closed container from which connection terminals protrude for the power supply of the control electronics.
The electrical machines used as a reference for this invention are in particular of the brushless enclosed type also known as the sealed type, that is, sealed electrical machines.
It is known that the windings of an electrical machine, whether they are stator or rotor windings, are made using a plurality of coils of conducting material, usually copper, made of a conducting wire wound around two or more pole shoes of the stator and/or the rotor of the electrical machine. The winding, through which electricity flows, is isolated from the pole shoes, which are made of ferromagnetic material. For that purpose, a layer of electrically insulating material is interposed between the winding and the corresponding pole shoe on which it is wound.
An electric current which may even have a high nominal value passes through the winding and that causes heating phenomena due to the Joule effect which extend over the entire dimensions of the winding and in the zones of the electrical machine adjacent to it.
In particular, it has been found that said heating phenomenon causes a deterioration of the conductivity properties of the conducting wire, which consequently produces a greater resistance to the passage of electric current, causing a high and often unacceptable level of energy dissipation.
Moreover, the heating of the winding may cause a rapid deterioration of the insulating characteristics of the above-mentioned layer of electrically insulating material interposed between the winding and the corresponding pole shoe, as well as excessive heating of the electronic module.
That situation is particularly bad in closed type rotary electrical machines, in which the windings are immersed in the container, formed by a casing and cap, which does not have air recirculation.
A solution intended to overcome said difficulty is described in the document WO2009019562 in the name of the same Applicant.
In that solution, the inside of the casing is provided with a plurality of stop portions, in the form of protrusions of a base wall of the casing, against which the stator windings abut, suitably insulated, for more effective heat exchange with the cap.
In the case of high powered motors, at around one kW, the prior art solutions are still not completely satisfactory in terms of dispersing the heat produced in the windings.